1. Field of the Invention
The present invention relates to a dielectric chip antenna of the type used in portable terminals and radio communication devices.
2. Description of Related Art
Conventional dielectric chip antennas of the type referred to above are configured in such a manner that a single radiation electrode is formed on an outer surface of a dielectric substrate so as to assume a spiral or wound shape. One end of the radiation electrode is connected to a feeding or feed electrode, whereas the other end of the radiation electrode serves as a free end (see Japanese Patent Application Laid-Open (kokai) No. 2000-13126).
Laminated-type dielectric chip antennas are also known (see, e.g., Japanese Patent-Application Laid-Open (kokal) Nos. 9-51221 and 9-55618). These conventional laminated-type dielectric chip antennas are configured in such a manner that a plurality of dielectric layers each carrying a conductor line or element formed thereon are provided, and the conductor lines of the dielectric layers are electrically connected together by means of through-holes.
With increasing demands with respect to miniaturization and performance enhancement of portable terminals and radio-communication devices, chip antennas of the above-described types have been increasingly required to be of smaller and smaller sizes while also having a broader bandwidth.
In the latter regard, the bandwidth BW of a chip antenna can be represented as follows:
BW=kxc2x7(C/L)xc2xd
where L is the inductance of the antenna conductor, C is the capacitance between a capacitance generating conductor and ground, and k is a constant. Therefore, the bandwidth BW becomes broader, i.e., is greater, when the capacitance C between the capacitance generating conductor and ground is increased, and when; the inductance L is reduced.
Conventional chip antennas as described above cannot satisfactorily meet both the requirements of reduced size and broadened bandwidth. Further, during the assembly of conventional chip antennas, when a worker mounts such a small chip antenna onto a printed circuit board, the worker must check whether the upper side or lower side (i.e., front side or reverse side) of the chip antenna faces upwardly, thus adding a cumbersome step to the assembly process.
In view of the foregoing, an object of the present invention is to provide a dielectric chip antenna which can meet both the requirements of reduced size and broadened bandwidth.
Another object of the present invention is to provide a dielectric chip antenna of a construction which facilitates mounting thereof onto a printed circuit board.
In order to achieve the above objects, in accordance with the present invention, there is provided a dielectric chip antenna comprising a substantially rectangular parallelepiped dielectric substrate; a feeding electrode for receiving high-frequency energy to be transmitted by the antenna, the feeding electrode being disposed on one longitudinal end surface of the dielectric substrate; a fixation electrode to be used for fixation of the dielectric chip antenna, the fixation electrode being disposed on the opposite longitudinal end surface of the dielectric substrate; and first and second radiation electrodes formed on a peripheral surface of the dielectric substrate so as to extend longitudinally while spirally surrounding the dielectric substrate, base ends of the radiation electrodes being connected to the feeding electrode.
Preferably, the two radiation electrodes are connected to the feeding electrode on opposite lateral side surfaces of the dielectric substrate.
Because the twb radiation electrodes connected to the feeding electrode are formed so as to spirally surround the dielectric substrate, the center frequency of the antenna can be shifted downwardly, i.e., to a lower frequency, by about 10 % as compared with a chip antenna wherein a single radiation electrode is spirally wound around a dielectric substrate, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2000-13126, where the dielectric substrate is of the same size. Therefore, with the construction of the invention, the overall size of the dielectric chip antenna can be reduced. Further, because the capacitance C between the capacitance generating conductor (radiation electrode) and ground can be increased, the bandwidth of the antenna can be broadened.
Preferably, the two, radiation electrodes are formed symmetrically with respect to a horizontal plane passing through a center axis of the dielectric substrate, so that the two radiation electrodes form identical patterns on the upper and lower surfaces of the dielectric-substrate.
With such a construction, a worker can mount the dielectric chip antenna onto a printed circuit board without checking whether the upper side or lower side of the chip antenna faces upwardly. Therefore, the effort required in mounting the dielectric chip antenna can be significantly reduced, i.e., the cumbersome step of determining whether the upper or lower side of the substrate faces upwardly can be eliminated.
More preferably, the feeding electrode extends an equal amount onto the upper and lower surfaces of the dielectric substrate.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.